This invention relates to torque wrenches used for rotating mechanical components, e.g. for tightening or loosening nuts, bolts and screws.
Generally these wrenches use a wrench head, for example a removable standard socket spanner, carried by holding means on the wrench, normally a shaft mounted rotatably in a housing. As an alternative, special sockets may be used, these sockets having a polygonal bore for the nut or other polygonal head to be rotated by the wrench and a shaft which fits into a hole in the wrench, this hole then constituting the holding means for the socket. At least one drive lever extending radially from and pivotable coaxially with the said holding means is connected to it by a ratchet, and a piston rod of a reciprocating fluid piston cylinder arrangement is pivotally connected to the drive lever or levers at a location radially spaced from the said holding means, to oscillate the lever and thus drive the said holding means in rotation through the ratchet.
Since in most known arrangement the drive lever oscillates in an arc about the axis of the said holding means, the distance between the line of action of the piston rod and the said axis varies throughout the oscillation. In theory when a constant force is applied the torque exerted on the said holding means is proportional to this distance.
U.S. Pat. No. 4,027,561 shows a torque wrench of this kind in which the hydraulic cylinder is pivoted at the end remote from the drive levers to accommodate the arcuate movement of the end of the piston rod remote from the cylinder, the piston rod itself reciprocating on the axis of the cylinder. In FIGS. 1 to 3 of United Kingdom Pat. No. 2,028,204,B the cylinder bore is formed in the housing of the wrench so that the cylinder has a fixed axis and the piston rod is swivelably mounted in the piston, again so as to accommodate the movement of the far end of the piston rod in an arc round the shaft axis.